The present invention relates to the art of microelectronic packaging and more particularly relates to packaged semiconductor chip assemblies suitable for mounting on substrates such as circuit panels, and to methods of making and using such assemblies.
Semiconductor chips commonly are connected to other elements of an electronic device by mounting the chip on a substrate such as a circuit panel having electrical conductors extending along its surfaces or within the substrate structure. In some cases, the chip is mounted in a package having external conductive elements such as leads or pins protruding from the package. A socket may be mounted to the substrate and the external leads or pins of the chip package may be received in the socket. In other arrangements, the chip package may have solderable contacts on a surface of the package, and may be mounted directly to the substrate by soldering techniques commonly referred to as surface mount technology. In these soldering techniques, each contact on the package directly abuts a contact pad on the substrate, and is bonded thereto by solder masses carried on the package or on the substrate. In other techniques, a bare unpackaged chip can be placed directly on the circuit panel and connected to the electrical conductors of the panel by techniques such as wire bonding, tape automated bonding (TAB), or flip-chip bonding. In flip-chip bonding, the front surface of the chip faces downwardly toward the surface of the substrate, and contacts on the front surface of the chip are directly bonded to contact pads on the substrate surface, as by solder disposed between the contacts and pads. The entire assembly is then packaged, as by encapsulating or partially encapsulating the substrate and chip.
In many cases, it is desirable to provide a metal cap covering the chip, the chip being bonded to the substrate. Such a cap can serve as a thermal spreader, and can conduct heat generated by the chip during operation away from the chip. For example, in a flip chip arrangement, the cap may provide a thermal path from a rear surface of the chip, facing away from the panel, to the circuit panel. The metal cap may also provide an electrical interconnection to the rear surface, as where the rear surface is used as a ground or power connection. Also, the cap can provide additional mechanical protection and additional electrical shielding around the chip. Typically, such caps have been added in separate operations after the chip is mounted on a circuit panel, which have required additional steps beyond those needed to mount the chip. Moreover, the metal caps and other components used in attaching the metal caps to the chips and circuit panels must be stocked and handled separately. All of this adds cost and complexity to the circuit panel manufacturing process. Accordingly, there have been needs prior to the present invention for improved chip assembly procedures which avoid the need for separate handling of the metal cap during assembly of the circuit panel, and there have been corresponding needs for prepackaged chip assemblies which can be utilized in such simplified procedures, as well as needs for methods of making such chip assemblies.